Woven thermoplastic materials such as nylon and Dacron and many others have been commercially available for many years. Because of the differences between such materials comprised of thermoplastic filaments and those of natural fibers, it has been necessary to develop many special techniques for working with such materials. Several of these problems stem from the slippery nature of the filaments themselves, which characteristic causes the woven materials to ravel and fray readily when the material is cut or severed.
To overcome these problems, various techniques and apparatus incorporating the use of heat have been developed such that the various filaments of the thermoplastic material may be fused together during the severing in order to restrain such raveling. Exemplary of such apparatus are those that have been disclosed in various patents, such as U.S. Pat. Nos. 3,931,491, 3,808,672, 3,880,201, 3,313,323 and 3,174,515. One patent of particular interest is that to Siclari et al, U.S. Pat. No. 3,757,077. This patent discloses an arrangement for cutting strands of fibers which are held between two belts and exposed to a laser beam through apertures in at least one belt. However, the Siclari apparatus does not address one of the principal problems of the application of heat to such a cutting operation. Specifically, the prior art apparatus provides no means for restraining the flaring of the ends of the filaments which commonly occurs when heat is applied to such filaments.
The flaring problem common to heat sealing the ends of such thermoplastic filaments is undesireable for materials that may come in contact with articles of clothing, since the flared filaments tend to present a rough surface to the severed end of the material, thus presenting a substantial danger of snagging clothing which comes into contact with such rough, heat-sealed cuts. This problem has been quite common in the manufacture of automotive seat belts in which the belts are cut from lengths of woven nylon webbing. Heretofore the severed ends of such seat belts frequently presented an undesirably rough surface which may be damaging to the clothes of users of such belts.